The residual stress predictions from sequentially and fully coupled thermo-mechanical generalized plane strain models of thick multipass welded plate are shown to be in agreement with each other and experimental data. The research enabled the less computationally resource intensive sequential coupling method to be recommended when simulating this welding process.

This article discusses the influence of various process parameters on the characteristics of titanium dental implants made by laser-forming techniques involving both laser sintering and laser melting. The implant models have a porous surface structure to increase bone-osseointegration and a compact core to provide the required mechanical strength. Models in the shapes of rod and cone were built using a continuous wave (CW) laser yielding a threshold compressive force as high as 1000 N after a postsintering treatment in a vacuum furnace at 1200°C for 1.5 h. Using selective laser melting with the pulsed laser, the best parameters were found to be: scan speed of 6 mm/s, laser peak power of 1 kW, and hatching pitch of 0.4 mm yielding a tensile strength of 300 MPa and torsional fatigue strength of 100 MPa. To improve the surface wear resistance of the titanium models, laser gas nitriding using CW Nd:YAG laser was applied. The formed TiN layers had a sponge-like structure with a thickness varying from 30 to 60 μm. The hardness measured at ε20 μm from the surface varied from 1000 to 600 HV by changing the scan speed from 1 to 16 mm/s.

This overview will focus on the direct fabrication of metal components by using laser-forming techniques in a layer-by-layer fashion. The main driving force of rapid prototyping (RP) or layer manufacturing techniques changed from fabrication of prototypes to rapid tooling (RT) and rapid manufacturing (RM). Nowadays, the direct fabrication of functional or structural end-use products made by layer manufacturing methods, i.e. RM, is the main trend. The present paper reports on the various research efforts deployed in the past decade or so towards the manufacture of metal components by different laser processing methods (e.g. selective laser sintering, selective laser melting and 3-D laser cladding) and different commercial machines (e.g. Sinterstation, EOSINT, TrumaForm, MCP, LUMEX 25, Lasform). The materials and applications suitable to RM of metal parts by these techniques are also discussed.

Selective laser sintering (SLS) is one of the most rapidly growing rapid prototyping techniques (RPT). This is mainly due to its suitability to process almost any material: polymers, metals, ceramics (including foundry sand) and many types of composites. The material should be supplied as powder that may occasionally contain a sacrificial polymer binder that has to be removed (debinded) afterwards. The interaction between the laser beam and the powder material used in SLS is one of the dominant phenomena that defines the feasibility and quality of any SLS process. This paper surveys the current state of SLS in terms of materials and lasers. It describes investigations carried out experimentally and by numerical simulation in order to get insight into laser-material interaction and to control this interaction properly. (Emerald Publishing Group Limited)

A full three-dimensional (3D) thermo-mechanical finite element (FE) model has been developed to simulate the step-by-step multipass welding process. Non-linearities associated with welding, such as a moving heat source, material deposition, temperature-dependent material properties, latent heat, and large deformations, were taken into account. The model was applied to multipass butt-welded mild steel plate and girth butt-welded stainless steel pipe for validation. The simulation results were compared with independently obtained experimental data and numerical predictions from two-dimensional (2D) generalized plane strain and axisymmetric models. Good agreements between the 3D predictions and experimental data have been obtained. The computational model has the potential to be applied to multipass welded complex geometries for residual stress prediction. (Professional Engineering Publishing)

Coupled metallographic examination and heat transfer numerical simulation are applied to reveal the laser sintering mechanisms of Ti powder of 63-315?µm particle diameter. A Nd:YAG laser beam with a diameter of 2.7-5.3?mm and a power of 10-100?W is focused on a bed of loose Ti powder for 10?s in vacuum. The numerical simulation indicates that a nearly hemispherical temperature front propagates from the laser spot. In the region of a-Ti just behind the front, heat transfer is governed by thermal radiation. The balling effect, formation of melt droplets, is not observed because the temperature increases gradually and the melt appears inside initially sintered powder which resists the surface tension of the melt. (Emerald Publishing Group Limited)

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